Page 13 - ACE YR IGCSE A TOP APPROACH TO BIO

Use the guide provided to aid in using the dichotomous key to identify each species.

First
Fin spine dorsal fin

Second
dorsal fin

Caudal fin
Snout

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Mouth Anal fin
Gill slits Pelvic fin
Pectoral fin

1 (a) Anal fin present Go to 2

(b) Anal fin absent Go to 3

2 (a) Has two dorsal fins Go to 4

(b) Has only one dorsal fin Hexanchus griseus

3 (a) Long and narrow body Go to 5

(b) Body is flattened, ray-like body Squatina dumeril

4 (a) Has a dorsal fin spine Heterodontus galeatus

(b) Does not have a dorsal fin spine Go to 6

5 (a) Snout is elongated, saw-like Pristiophorus nudipinnis

(b) Snout is short and not saw-like Squalus acanthias

6 (a) Mouth is behind the eyes Go to 7

(b) Mouth is in front of the eyes Rhincodon typus

7 (a) Head is flattened Sphyrna mokarran

(b) Head is pointed and not flattened Isurus oxyrinchus

[Total: 8]

Chapter 1 Characteristics and Classification of Living Organisms 11

Chapter 1.indd 11 30/03/2022 3:07 PM